Telephone system



June 13, 1939.

R. E. HERSEY TELEPHONE SYSTEM Filed June 17, 1958 6 Sheets-Sheet 1 //vVEN TOR RE. HE RSE Y ATTORNEY June l3, 1939.

R. E. HERSEY TELEPHONE SYSTEM 3w e w 6 Sheets-Sheet 2 g V INVENTOR RE HERSE V BY WWW ATTORNE Filed June 17, 1938 June 13, 1939. R. E. HERSEYTELEPHONE SYSTEM Filed June 17, 1938 s Sheets-Sheet s xmw mumw mtwmmmuiko ILIII Jllli lNVE/VTOR REHERSE) A TTORNEV 5 SheetsSheet 4 R. E.HERSEY TELEPHONE SYSTEM Filed June 1'7, I938 INVENTOR REHERSEV 5r W WMJune 13, 1939.

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TELEPHONE SYSTEM Filed June 17, 1938 6 Sheets-Sheet 5 M/VE/VTOR mm 7 22242; $2,? REHERSEV ATTORNEY TELEPHONE SYSTEM Filed June 17, 1938 6Sheets-Shet 6 a t b g' llb V 9 F. 1 L fig J] l" E a \T I L. E a 12 8 'a1? 2 fiq n 6 E 7: a g 1?" 11' rll' ' 3 If, u S a!) I I b N l a; N

INVENTOR RE. HE/PS-EY A TTORNE V Patented June 13, 1939 UNITED STATESPATENT "OFFICE TELEPHONE SYSTEM Application June 17, 1938, Serial No.214,350 7 Claims. (Cl. 179-225) This invention relates to telephonesystems and particularly to those employing automatic switchingequipment for establishing conversational connections.

One of the advantages of automatic switching systems employing switchesof the cross-bar type and common markers for controlling their selectiveoperations is the facility with which the markers can be arranged totest and retest 10 all available circuit paths in an effort to establisha desired connection. These tests are made in so short a time that it ispossible and desirable to make second and even third trials to serve thewaiting call. And in some cases a group of trunks, if found busy on afirst trial,

may be retested a moment later in a second attempt to complete the samecall.

Another advantage of the cross-bar system is that the trunks of a groupmay be divided into two subgroups, one of which is located on one frameof switches and the other on a second frame of switches, the markerbeing capable of testing both subgroups simultaneously for the purposeof finding an idle one for use. To do this the marker connects itself tothe proper pair of switch frames through frame connectors and proceedsto test all trunks of the group, selecting the first idle one for use.Having found an idle trunk on a particular frame, the marker then makesa test of the link paths of that frame and, if an idle one of thesepaths is located, completes the connection through to the selected idletrunk.

With these facilities a high degree of efficiency is possible in the useof the available equipment for completing calls. In some cases, however,it is possible that a call may fail to be served, due to such causes asfaulty test connections, which may persist on subsequent as 4 well as onfirst trials, or the failure to find at the same time an idle trunk andan idle link path in the frame of switches on which such trunk appears.

The objects of the present invention, there- 45 fore, are to increasestill further the efiicient use of the equipment in these systems; toincrease the accessibility of calls to the trunks and connectingcircuits that serve them; to reduce the likelihood of failure because oftemporary ir- 50 regularities in the testing mechanism; andin otherrespects to improve these systems.

In accordance with these objects it is a feature of the invention toprovide a testing arrangement in the marker which acts, when'the 55marker is making a first trial to extend a call in which a common switchcontrolling marker makes repeated trials to extend a call by conover adesired group of trunks, to test the successive trunks in a definiteorder and to choose the first idle one for use, and which acts, when themarker is engaged in making a-subsequent trial to extend, the call, totest thewsuccessiv eu trunks of said group in the reverse order.According to another feature of the invention, when a callis receivedfor a given group of trunks, one subgroup of which appears in oneswitch'and a second subgroup in a second switch, ,10 each switch beingreached over separate groups of link paths, all trunks of the group aretested simultaneously to select an idle one in one or the other of thesubgroups, followed by a test of the link paths leading to the selectedtrunk; 15 and, if all these link paths are found busy, a retest is madeof both subgroups, all trunks being rendered artificially busy in thesubgroup that could not be reached because all link paths were busy onthe first attempt, causing thereby the selection of an idle trunk in theother subgroup if it contains one; and thereupon a test is made to findan idle link path in the group that has access to said other subgroup.With this arrangement a call for a trunk group is not 25 necting itselfsimultaneously to a pair of'switch frames and testing the desired trunkgroup, some "first trial to establish proper connection With the switchframes results in the release of the marker and the reseizure of thesame or another marker for a second trial; in whichthe marker on asubsequent trial, although failing to make 40 proper connection with oneframe, proceeds to test the desired trunk group; and in which all trunkson the frame to which the marker. failed to connect are renderedartificially busy in order to confine the selection of the idle trunkfor'use to the second frame, to which the marker succeeded in makinganoperative connection.

A clearer understanding of the purpose and scope of theinvention will beobtained from the following description in connection with the attacheddrawings in which:

Figs. 1 to,6, when arranged as seen in Fig. '7, show partly indiagrammatic form and partly in detail, a telephonesystem embodyingthefe'atures of this invention; s5

connectors;

Figs. 4, 5 and 6 illustrate one of the switch controlling markers;

Fig. 4 shows the test relays which test for an idle channel extendingthrough district and office link frames to an outgoing trunk;

Fig. 5 shows the relays that test for an idle outgoing trunk; and

Fig. 6 shows controlling relays that cooperate with other apparatus aswill be hereinafter described.

Before describing circuit operations in detail, it is advantageous toconsider the general features of the system.

A subscriber station I is connected over line IOI .with the primaryswitch I02 of the line link frame and thence over the link I03 with thesecondary switch I04, both of which switches are indicated inabbreviated diagrammatic form. The connection from the line link frameis extended over the district junctor I05, the control equipment ofwhich is illustrated at I06, to the horizontal conductors of primarydistrict switch 200. These horizontal conductors have access as shown,to any one of. a plurality of vertical district links 202, 203, 204,205, which extend to the secondary district switch 20I, and connectthereon with horizontals. These horizontals, although shown connected tothe same switch, may also be connected to several different switches.From the secondary switch 20I, district links 202, 203, 204, 205 areextended over ofiice junctors v206, 201, 208, 209, respectively, toswitches of a pair of oflice link frames, which frames, for purposes ofidentification, are in practice consecutively numbered. Accordingly oneof the frames will be identified by an even number, and the other by anodd number. Junctors 208 and 209 are shown extending to primary switch300 of the even numbered frame and junctors 206 and 201 to primaryswitch 30I of the odd numbered frame. The four junctors aforesaidconnect respectively to verticals on .the two frames. Junctors 206 and201,

which have access to horizontals of switch 3!,

are extended over. office links 304 and 305 to verticals of secondaryswitch 303, and junctors 208 and 209, which have access to horizontalsof switch 300, are extended over ofiice links 306 and 301 .to verticalsof secondary switch 302. Links 304, 305, 306 and 301 have access tohorizontals of the two switches which are connected with outgoing trunks3I4 and 3I3.'

Trunk 3I2 on the even frame, and trunk 3l5 on the odd frame, withoutconnections, are also shown. These trunks may be connected to otherhorizontals, not shown, to which the vertical links 36 and 301, and 304and 305 may also have access.

When the subscriber of station I 00 originates a call the connection isfirst extended over line IOI, through line link switches I02 and I04,con.

nectedbylink,I03, thence over district junctor I05 to the connectinghorizontal of district switch 200. The calling line is also extendedover con- 7 selected trunk must be determined. A channel consists ofthree serially connected elements, that is, a district link betweenprimary and secondary district switches, an office junctor betweensecondary district and primary oflice switches, and

an office link between primary and secondary ofiice switches.v Assumingthat an idle channel is found, the marker now operates the proper switchmagnets and effects the closure of four sets of switch'contacts, whichthereby complete the connection to the selected outgoing trunk.

Let it be assumed that the trunks are grouped for testing purposes inthe order 3I2 -3 I33I4- 3I5. The marker tests the trunks in this order.

If, for any reason, after the idle trunk has been selected, the markercannot complete the connection which thereby necessitates a secondtrial, the trunk test is made in the reverse order, that is,3I53I43I33I2.

If all channels leading to the selected trunk are found busy, then aretest of the group of trunks is made after all trunks on the frame thatcould not be reached the first time are made artificially busy. Forinstance, let it be assumed that trunk 3! on the even oflice frame hasbeen selected on the first test. When a test is then made to select anidle channel it is found that the channels which have access to thistrunk, and which terminate in office links 306 and 301 are busy. In aworking installation consisting, for instance, of ten district framesand five pairs of mated office frames there would be a maximum of twentypossible channels from each district junctor to each trunk, when onlyone trunk is assigned to a single horizontal on the office frame. Thetwo channels aforesaid are suflicient, however, to illustrate theoperation, and when these are found busy as hereinbefore stated, thenall trunks on the even numbered frame are made artificially busy.Accordingly trunks 3I2 and 3I4 are made to appear busy to the trunktesting relays which are shown in Fig. 5. One of the trunks 3I3 or 3I5on the odd numbered ofiice frame is then selected on the second test.Assuming that trunk 3I3 is selected, then a test for an idle channelextending to this trunk is made. A plurality of these channelsisrepresented by the channels terminating in oflice links 304 and 305.

If the marker is making a first trial and a failure occurs due to anopen test conductor extending to one of the pair of office frames uponwhich pair of frames is located the trunk extending to the calledoffice, then the marker will time out and send a trouble release signalto the sender. One of these testconductors is repre:- sented, forinstance, by conductor 308. If the connecting relay should fail tooperate properly andconductor 308 should not be connectedto ground 355,then the marker will'time out-as hereinbefore stated, provided it isfunctioning on a first trial. If the marker is engaged on a second orthird trial, however, and it encounters a failure of this nature,.itdoes not time outibut makes trunks 3I2 and 3M of the even numbered "(5frame appear busy to the trunk testing relays, since these trunks arelocated on the frame on which the assumed trouble in connection with thetest conductor 308 was encountered. The marker then proceeds to test thetrunks M3 and 3|5 on the odd numbered frame. If trunk 3 l3 should befound not busy, then the channels terminating in links 364 and 305,which have access to trunk 3|3, are tested, and, if one of these isfound idle, the connection is established to trunk 3l3.

While the system disclosed is not limited to the use of cross-barswitches of any particular type, reference may be had to the patent toReynolds 2,021,329 of November 19, 1935, for an understanding of theconstruction and operation of a switch suitable for use in such systems.Because of the complicated nature of these systems, and since it is notnecessary to an understanding of the invention that the system in all ofits details be disclosed, much of the circuits and equipment has beeneliminated in the present disclosure for the sake of simplicity. And inthe following descriptions reference will be made to numerous operationswhich are not fully disclosed in all of their details. Wherever suchreferences occur it will be understood that the circuits and equipmentso referred to are already known, and in particular reference is heremade to the following for a detailed disclosure of all operations andequipment referred to herein but not specifically disclosed: CarpenterPatent 2,093,117 of September 14, 1937; and Carpenter application SerialNo. 214,356, filed June 17, 1938.

The operation of the system will now be described in detail. When thesubscriber of station I originates a call over line llll, cross-barswitches 02 and Hit of the line link frame function, extending line itthrough link N33 to the district Junctor I 05. Junctor 195 is thenconnected to sender I68 over a plurality of conductors Hi9 by means of asender selector mechanism I I9, represented by a conventionalabbreviation. The connection from station ififi is also further extendedover the district junctor to a horizontal of primary district switch280. At this time select magnet 2N1 corresponding to this horizontal iscaused to operate over a circuit, not shown, extending from junctorcontrol circuits I05. When the subscriber of station Hit! has dialed thecode of the ofiice to which the call is to be extended, sender I03,having received and registered this code, is connected to an idle markerby a conventionally represented connecting device I l l over a pluralityof conductors represented by the line H2. The sender in response to therecorded office code then selectively operates certain relays, notshown, in the marker and causes thereby the selective operation of relaySIS of the office frame connector associated with the even frame, and ofrelay 3! 9 of the office frame connector of the odd frame. These relaysare selectively operated because they are associated with frames onwhich are located the trunks 3l2, SIS, 3M and 3l5 extending to thecalled office. Relays 3! 3 and 3l9 in operating operate, with their leftcontacts, associated relays 329 and 32!, through circuits not completelyshown. Relays 3| 8 and 3l9 effect the closure of trunk testingconductors 324 and 325, and 326 and 321. Relays 320 and 32! connect tothe marker the testing conductors for office links 394, 395, 306 and301. As will be hereinafter explained, when the particular office frame,even or odd, upon which the selected trunk is located, has beendetermined, then the relay 329 or 32| corresponding to the frame whichis not to be used for the call, is released, to avoid interference.Consequently the test conductors are used for both frames, but for onlyone frame at a time.

With the operation of relays 3 l8 and 3! 9 which closed the trunktesting conductors as hereinbefore described, the marker proceeds totest for an idle trunk in the group of trunks Referring toFig. 5, itwill be observed that there are shown four files of testing relays, eachfile corresponding to a trunk. Relays 50c, M, 5412 and 5533 are used fortrunk 3l2 on the even frame, relays 504 to 587 for trunk M3 on the oddframe, relays 508 to 5! l for trunk 3 E4 on the even frame and relays5l2 to M5 for trunk M5 on the odd frame. For a working installationprovision is made to test trunk groups containing a maximum of fortytrunks, twenty trunks being assigned to the even numbered and twenty tothe odd numbered frame of a pair of frames. Accordingly it is to beunderstood that between relay files, 5645fi1 and 508-5ll there shouldbe, on the basis of forty trunks maximum, thirty-six additional relayfileseighteen assigned to even, numbered frames and eighteen to oddnumbered frames. Although a maximum of forty trunks in a group may beprovided, any smaller number may be used. In general, groups containingan,

even number of trunks are used, the even numbered trunks being assignedto the even numbered frames and the odd numbered trunks to the oddnumbered frames.

In the case of groups containing an odd number of trunks, one additionaltrunk terminal on one of the switches is grounded artificially tomaintain the symmetry of the testing chain.

Returning now to the test of the trunks the marker must indicate beforestarting the test the beginning and end of the group of trunks extendingto the called office. This result is obtained by grounding two of thewinding terminals 525, 52!, 522, 523, one of the terminals groundedcorresponding to a relay test file assigned to the even frame and theother to a file assigned to the odd frame. With this arrangement anyeven number of trunks from two to forty in a test group may be providedfor, and the beginning and end of the group may be located at any pointas required by the location of the trunk group on the ofiice frames. Letit be assumed now, for the purpose of this description that the markergrounds terminal 520 of relay 5:39, and terminal 523 of relay 5H2,marking thereby the group start and group end points respectively, thattrunks 3l2 and M5 are busy due to ground being connected to their sleeveterminals, and that trunks 3l3 and SM are idle. The aforesaid groundingof the sleeve conductors is effected by the closing of their associatedswitch contacts and is illustrated for trunks M3 and 3 l4, when grounds353, 359 and 355, 35?, respectively, are thus connected to theassociated sleeve conductors. The operation of the system whereby anidle trunk is selected will now be discussed.

The grounding of terminals 520 and 523 causes the operation of relays50!] and H2, which lock through their lower contacts and a circuit, notshown in full, to ground 524. Ground connected to the sleeve terminal oftrunk M2 is extended through next to innermost contacts of relay 318,over conductor325, through lower inner contacts of relay 503 and windingof relay 502 to battery. Relay 502 operates and closes an obviouscircuit for relay 50!, which operates and disconnects with its upper andlower break contacts the winding of relay 503, preventing the subsequentoperation of this relay. In like manner, relay 3i9 in operating connectsthe sleeve conductor of trunk 5l3, with its innermost contacts, toconductor 321 and thence through lower break contacts of relay 501 tothe winding of relay 506. Since by assumption, trunk M3 is not busy,there is no ground on its sleeve terminal and consequently relay 506and, in turn, relay 505 do not operate. Relay 501, however, does operatenow from battery through a circuit path left break contacts of relay5l9, winding of relay 551,

upper break contacts of relay 505, operated upper make contacts of relay50L upper inner operated make contacts of relay 500, over conductor 525,through upper, outer break contacts of relay 655 and over conductor 6E9,through operated contacts of relay 6 l1, over conductor 612 and throughupper operated contacts of relay 6H} to the contactsof relay 659. RelayH1 or BIB operate when even or odd numbered district frames,respectively, are engaged and are used so as to reverse the direction oftesting through the trunk testing circuit. When conductor 525 isconnected to conductor EIZ, then the direction of testing is in theopposite direction to that used when conductor 525 is connected. Thisarrangement evens the wear on the trunk testing relays.

Relay 5|0 operated, when the marker was first engaged, over conductor521 and through upper normally closed contacts of relays 515, 5, 501 and503 to ground 532. Relay 509 is slow to operate, so as to give ampletime for the operation of any of the relays, 502, 505, 5), 5M, beforetheir operating circuits are opened by relays 503, 551, 5! I, 5|5,respectively. When the marker is engaged for the call, the upper andlower windings are energized, but relay 609 does not operate because ofthe differential connection of the windings. The circuit of the upperwinding extends from battery through the winding of relay 559, lowerbreak contacts of relays 505 and 601 in multiple, to ground through thelower multipled break contacts of relays 606 and 508. The lower windingof relay 609 is energized from battery through resistance 6H to ground.The group of trunks represented by trunks 3! 23 l33l43l 5 may bearranged on either a split or non-split basis. If arranged on a splitbasis then the horizontals of the switches are cut in the middle and onehalf of the trunks are connected to the left horizontals and the otherhalf to the right horizontals. Assuming that the split arrangement isused, then relay 3l8 of the even frame in operatlng' connects ground 355with its outermost contacts to conductor 358, operating thereby relay606 which in operating disconnects ground 5M. In like manner relay 3L9of the odd frame connects ground 354 to conductor 3H3, operating relay600 which disconnects ground (H3. The circuit of the upper winding ofrelay 505 is now open and relay 509 operates slowly, being energized bythe current in the lower winding. Should the trunks be arranged on anon-split basis, then the horizontal switch conductors are not cut andeach trunk of the group uses an entire switch horizontal; With thisnon-split arrangement relay 3 I B in operating connects ground 352 toconductor 309, operating thereby relay 555. Relay Hi9 connects ground353 to conductor 3H, operating relay 601. The circuit of the upperWinding of relay 609 is also thus opened by the for a second trial.

operation of relays 605 and 601.- It must be explained that circuits notshown here are-provided so that the pairs of relays 506 and 608, and 605and 601 are operated regularly only when their Relay 609, when'itfinally operates, connects ground to the winding of relay 501 over thecircuit here'mbefore traced. Relay 501 in operating looks through itsupper make contacts to ground 532 through normally closed contacts ofrelay 503. This disconnects ground from the winding of relay 5E0, whichreleases, thereby opening the operating circuit of, relay 501, whichreamins looked through the circuit before described. The release ofrelay Bill also connects ground, with its lower break contacts, to theupper winding of relay 509, thereby reestablishing the originaldifferential condition of the two windings of relay 555, whichaccordingly releases.

When relay 501 operated as before described, it was an indication thatthe corresponding trunk 3E5 on the even oflice frame was idle. Relay 501in operating opens, with its lower break contacts, the circuit of relay505. Let it be assumed now that the marker, because of some troublecondition cannot complete the call. Afterthe timing mechanism 4 hasmeasured an interval of time, the sender Hi3 receives a trouble releasesignal, the marker is released, and immediately a second trial is made,with either the same or another marker. The trunks are again tested bythe second-trial marker. Assuming, as before, that trunks M2 and 355 arebusy and trunks H3 and 3M idle, test relays 502 and M operate, and

1 test relays 505 and 5H] remain deenergized. For

this second trial condition a circuit is closed for operating relay 852,which extends from battery through the winding of relay 502, breakcontacts of relays 555 and 503 and a circuit path to ground. Relay 552in operating closes, with its make contacts, a circuit for operatingrelays 600 and GUI. Relay 555 in operating transfers with its uppercontacts conductor-SIB from its normal connection with conductor 525 toconductor 526. Ground on conductor 525 is connected through the upper,inner operated make contacts of relay 512, lower operated make contactsof relay 513, (which is operated because trunk 3I5 is assumed to bebusy), lower break contacts of relay 509,,

winding of relay 5H and left break contacts oi relay M8 to battery.Relay 5H operates and locks to ground 532 through its upper make contacts and a series circuit through normally closed upper contacts ofrelays 50'5 and 503, and of retrunk M5, and not nearest to end trunkBIZ, as V are all tested simultaneously, as above explained, by the testrelays shown in Fig. 5. After the test relays have had time to operate,the chain test circuit, grounded by the relay 559, as described; isextended over conductor. 525 through the contacts of the successive testrelays, beginning at On a first trial the trunks the left, representingbusy trunks until the first .7

idle trunk is reached. This chain test circuit in effect examines eachsuccessive trunk in the group, beginning at one end, until it finds anidle one. And this idle trunk is the one that is taken for use. When asecond trial is made, however, the relay 600 is operated as explained,and, after the simultaneous test of all trunks has been completed, thechain test circuit now extends over conductor 526 which proceeds throughthe contacts of the test relays, beginning at the right in Fig. 5, untilthe first idle trunk is reached. Thus the successive trunks of thetested group on a second trial are examined in the opposite direction,until an idle one is found.

If, instead of grounding terminal 520 of relay 500 of the extreme leftfile of test relays shown in Fig. 5, terminal 522 of relay 508 isgrounded so that the group start point corresponds to the relay file,consisting of relays 508, 509, 5!!! and 5! I, then all relay files tothe left of this last-mentioned file are rendered ineffective. If any ofthe trunks beyond the limit of the test group should be busy then theirrelays 502, 506, etc. will be operated, causing associated relays 50!,505, etc. to operate. None of the selecting relays 503, 501, etc. can,however, find a path to operate through either operated or non-operatedcontacts of the relays 50!, 505, etc. due to the non-operated conditionof the upper inner make contacts of the relays 500, 504, etc.

Having thus described the trunk selection feature it is now in order todiscuss the means whereby an idle channel extending between districtjunctor I05 and the selected trunk is selected and established. Fig. 4has four files of channel testing relays, each file arranged to test acorresponding channel. Usually, however, provision is made to test amaximum of twenty chan nels. To facilitate this description the files ofrelays in Fig. 4 between the ends and two middle files are omitted andthe omission is indicated by broken lines. Relays 404, 405, 406 and testthe district link and oflice junctor, and relays 403, 409, M0 and 4!!the office link of each channel. In order to provide for installationswhere there are fewer than twenty channels, lower windings are furnishedfor relays 408, 409, 4!!) and 4! I. These relays are then operated bycircuit arrangements not shown, through these lowor windings, wheneverthe corresponding channel is not available, which has the effect ofblanking out the missing'channel as if it were busy. The selection of aparticular channel is indicated by the operation and locking up of thecorresponding relay 400, 40!, 402 or 403. The relays of Fig. 4 are usedto test channels extending to either the even or odd office frames. Whenrelays 2I3 and 320 associated respectively with the district and ofiiceframe connectors, are selectively operated, the test conductors areconnected to channels extending to the even frame. Relays 2| 4 and 32!are selectively operated when it is desired to test channels extendingto the odd frame. Since there are shown only two complete channelsextending to each of the two frames, battery connections to conductors230 and 23!, 236 and 23?, 332 and 333, 338 and 339, associated withrelays 2I3, 2I4, 320 and 32! are shown in order to indicate a completeworking arrangement for each file of channel testing relays of Fig. 4.

Let it be assumed that trunk 3!3 connected to the odd oflice frame hasbeen found idle as before described. It is now a function of the markerto test the channels extending to this nection from the district junctorI05 may be extended. When trunk 3!3 was selected, relay 50'! operatedand looked as before described, and

connected ground through its lower outer contacts over conductor 424 tothe winding of relay 4! 3, which operated. Relay 4 l 3 is identifiedwith the odd office frame and in operating opens a circuit extendingfrom ground 4 I 8 through break contacts of relays M5 and M3 overconductor 322 and through the winding of relay 320 to' battery on theleft operated contacts of relay 3I8. Relay 4l3 also in operating,effects the operation of relay 2!4 in a circuitover conductor 2I9,contacts of relay 4l3, conductor 443, to ground through the contacts ofrelay 5 I 9, and relay 2 I 4 closes the test conductors for junctorsextending to the odd office frame. Relays 320' and 32!, were previouslyselectively operated when, in response to information received fromsender I08, certain relays, in the marker were operated" indicating thatthe outgoing trunks to the called destination would be found on a pairof even and odd office frames with which relays 320 and 32! wereidentified. Relay 320 is identified with the even ofiice frame and whenit releases due to the opening of its operating circuit as before de-'scribed, test conductors 332, 333, 334 and 335 are disconnected in orderto avoid interference with test conductors 336', 331, 338 and'339'extending to the odd ofiice frame on which is located the selectedtrunk 3!3 and to whichan idle channel is to be selected.

When the channel test conductors are connected through to theirrespective test points, relays 404, 405, 406 and 401 operate, throughbreak contacts on relays 400, 40!, 402 and 403,

respectively, if the connected district links or: oflice junctors,either or both, are busy as evi-- denced by the presence of ground ontheir respective sleeve conductors. Similarly, relays'408, 409, 410 and4!! operate if their respective office links are busy. Let it be assumednow, as' a basis for description, thatthe'channel consisting of districtlink 203, ofiice junctor 20I'and ofiice link 304 is idle and that allother channels are busy. After the test conductors have been connectedfor a. short interval, which interval is sufficiently long to insure theoperation of all test relays that are going to operate, relay 4!!operates, through a circuit not shown in full, connecting ground 420 tothe armatures of relay 404;

circuit for relay 400 is kept open at either or both of the breakcontacts of these relays, and ground 420 is further extended to thearmatures of relay 405 through a series path consisting either of themake contacts of relay 404 or break and make contacts ofrelays 404 and408-and contacts of intervening relays, not shown. By previousassumption the channel corresponding to relays 40!, 405 and .400 is.idle and consequently the. ground on the armatures of relay 405'isextended. through break contacts, of relays 4'05 and 409 to the windingof relay 40!, which operates and locks through its lower, outer makecontacts and With either or both of the relays 404 and 408 operated,the" trunk, and select an idle one over which a con- I nels are busy ornot. Relay 401 in operating transfers to ground 422, with its innertransfer contacts, conductors 21'! and 258 from the wind ings of relay405, and with its uppermost transfer contacts conductor 330 from thewinding of relay 409. Ground 422 on these three conductors effects theoperation of the holding magnets 225 and 226 on the district frame, and341 and 340' the corresponding relay 511 is operated. This relayconnects grcund with its lowermost contacts to conductor 425, operatingrelay 414, which disconnects ground 419 from the contacts of relay 412and conductor 323, releasing relay 5-3321, which disconnects testconductors 336, 331,

338 and 339 extending to the odd oflice frame, thereby avoidinginterference with corresponding test conductors, 332, 333, 334 and 335,connecting with the even frame.

Relay 213, which connects the test conductors for oflice junctors'extending to the even frame on which is located the selected trunk 314,is selectively operated, through a circuit extending over conductor 222,contacts of relay 4'14, coniductor 442, to ground at the contacts ofrelay 518. Let it be assumed now that the channel consisting of districtlink 204, oflice junctor 238, and office link 30'! isavailable, and thatchannels corresponding to relays 400,404 and 408, to intervening relaysomitted, and to relays 401, 405 and 409 are busy, channel testing relays402, 4136 and 410 now function to select the aforementioned channel inthe manner before described in connection with the selection of achannel tending to trunk 313 on the odd frame. I

In the description heretofore given it was assumed that an idle channelleading to the se lected trunk could be found. If, however, fol lowingthe selection of the idle trunk. it happens that no idle channelextending to the selected trunk can be found, then the marker reteststhe trunk group, first causing the test relays of Fig. 5 to function asif all trunks on the frame to which no idle channel could be found, werebusy. Having again found an idle trunk this time, on the other frame ofthe pair, the marker then repeats the channel test to select if possiblean idle channel extending to. this second trunk. This feature will nowbe described in detail.

, Let it be assumed now that trunk 313 on the odd office frame wasselected as beforedescribed, and that the channel testing relays of Fig.4 functioned to indicate that all channels were busy. With all channelsbusy, relay 416 is operated in a circuit-extending from battery throughthe winding of relay 416, and thence through a series chain of contactsto ground 420. This series circuit extends through the lower makecontacts of each operated relay 401. 4015, 405 and 404'. When one ofthese relays is not operated, its associated relay 4| I, 410, 409 or 408must be operated because the channel is busy, and then the circuit iscompleted by way of the lower make contacts of the operated relay andthe upper break contacts' of the associated non-operated relay to ground420 through contacts of relay 411.

When trunk 313 was selected relay 501 operated and locked and effectedthe operation of relay 4'13 which operates when the selected trunk is onthe odd ofiice frame. Relay 413 connects ground to conductor 429 throughthe lower make contacts of relay 413, thereby operating relay 519, whichdisconnects battery with its left contacts, from the windings of relays59'! and 515 associated with the odd frame, with its right inner makecontacts relay 516. and with its right inner break contacts disconnectsground from conductor 443, thereby releasing relay 214, whichdisconnects conductors 234, 235, 236 and 231, which test the junctorsextending to the odd office frame. Relay 519 also looks to ground 531through its right outer contacts and a circuit not shown in full. Ground531 is connected in re sponse to the satisfactory operation of theconnecting relays 318 and 3| 9. The operation of relay 516 connectsground, with its right make contacts to the windings of relays 505 and513, associated with the odd office frame and in like manner to thewindings of all other similar relays, not shown, which are associatedwith the odd frame. Each of these relays now operates, if not alreadyoperated, due to the busy condition of their associated trunks. This hasthe effect of making each trunk of the subgroup located on the oddoflice frame test busy on the subsequent retest.

When battery was disconnected from the winding of relay 507, this relayreleased and in turn released relay 413. The release of relay 413connected ground 418 through break contacts of relays 415 and 413 toconductor 322, thereby reoperating relay 320 of the even oflice frame,which relay was released when the trunk 313 of the odd ofiice frame waspreviously selected. Relay 320 in operating connects test conductors332, 333, 334 and 335 to the channel testing circuit of Fig. 4. Theseconductors test the office links of the even frame. In'response to therelease of relay 214 heretofore described, relay 41'1 releases,disconnecting ground from 420 from the channel testing circuit.

With all trunks on the odd oflice frame responding as busy to the testcircuit of Fig. 5 and assuming that trunk 314 of the even frame is idle,relay 511' operates through left break contacts of relay 518 ashereinbefore described in discussing the trunk testing feature. Relay511 locks to ground 532 through its upper contacts and the series chainconsisting of the normally closed contacts of other similar relays. Withits lower make contacts, it connects ground to conductor 425, therebyoperating relay 414 associated with the even frame. Relay 414, with itsbreak contacts disconnects ground 419 from the break contacts of relay412 and conductor 323, thereby releasing relay 321 which disconmeets theconductors 336, 331, 338 and 339 which test the ofiice links of the oddframes, thereby preventing interference when subsequently testing thecorresponding links of the even frame. Relay 414 in operating alsoeffects the operation of relay 213, which connects the conductors fortesting the junctors extending to the even ofiice frame. After aninterval suflicient to insure the satisfactory closing of all thechannel test conductors, relay 41'1 operates and connects ground to theseries contact chain of relays 404, 405, 406 and 40?. Assuming now thatthe channel consisting of district link 204, ofiice junctor 208, andofiice link 30'! is idle and that channels corresponding to relays 400,404, 408 to intervening relays and to relays 40!, 495, 455 are busy,then relay 452 will operate through the series contact circuitterminating in ground 42s, as before described. Relay 452 in operatinglocks to ground 42! and transfers conductors 225 and 22! from thewindings of relay 455, and conductor 33! from the winding of relay MB,to ground s23, thereby effecting the operation of holding magnets 238,239, 346 and 341. Since select magnets 2H3, 221, 348 and 349 are alreadyoperated, cross-points 24B, 24!, 35B and 35! are closed, therebycompleting'the connection from district junctor I05 to the outgoingtrunk 3M.

In the foregoing the operation involving the testing of a group oftrunks, the selection of an idle trunk, the testing of the idle channelsextending to the selected trunk and the selection of an idle channelwere described. There is still another feature whereby the marker isarranged to determine whether it has been connected to the office framesand, if on the first trial there is a failure to connect to one of theframes, to time out and send a trouble release signal to the sender.However, if the aforesaid failure to connect to one of the frames occurson a second or third trial of the marker, the marker instead of timingout as on. a first trial now causes the trunk testing circuit toconsider busy all trunks connected to the frame in trouble, and to testthe trunks on the other frame. This feature will now be described indetail.

Referring now to Fig. 6, relays 695 and 606 are connected overconductors 309 and 358 respectively with contacts of the connectingrelay MS of the even oflice frame and relays fill! and 698 are connectedover conductors 3|! and M6 with contacts of connecting relay 3|9 of theodd office frame. The horizontal conductors of each oiiice frame may becut in the middle providing socalled split horizontals with thisarrangement: one trunk may be connected. to the left half, and anothertrunk to the righthalf horizontal, there being accordingly two trunksfor each split horizontal level. Where the horizontals are not splitthere will, of course, be only one trunk for each level. For each groupof trunks there must be either the same split or non-split arrangementon both frames, not both arrangements. Consequently, for any particulargroup of trunks, relay 605 may be assigned for the non-split and relay606 for the split arrangement on the even office frame and similarlyrelays 601 and 658, respectively, may function for the odd frame.

Let it be assumed now that the trunks are arranged on a split levelbasis. With this arrangement, when connecting relay 3!!! operates,conductor 388 is connected to ground 355 operating relay 60%, but ground352 is left unconnected at this time so that relay 685 does not operate.When relay 3!!) operates ground 354 is connected to conductor 3H5operating relay 658, but ground 353 is left unconnected so that relay607 does not operate. Assuming that relays 556 and 558 operate asstated, indicating the satisfactory functioning of relays H8 and 3l9 andthereby the satisfactory connection of the marker to both office frames,grounds 663 and 6M are disco-nnected from conductor M5 by the lowerbreak contacts of relays 588 and 6115, thereby removing ground from thelower multipled break contacts of relays 695 and 65'! and the winding ofrelay 6B9. Relay 659 now operates as before described and connectsground through its own contacts, operated contacts of relay 510, overconductor 5l2 through operated contacts of relay 6|! to the uppertransfer contacts of relay 600. If the marker is functioning on a firsttrial, relay 505 will be normal and connection will be made to conductor525, discussed hereinbefore.

If the trunks are arranged on a non-split basis, then grounds 352 and353 are connected by the operation of relays 318 and M9, groundingrespec tively conductors 309 and 3H, assuming that these relays operatesatisfactorily. Relays 6G5 and 60'! now operate and disconnect thegrounded conductor 515 from the upper winding of relay 659, whichoperates as before, starting the trunk testing circuit of Fig. 5.

The before-given discussion assumed that relays M8 and 3H! operatedsatisfactorily. Assume now that the trunks are arranged on a non-splitbasis and that relay 505 fails to operate, indicating that relay 3H8 hasfailed to effect a proper connection to the even office frame. Althoughrelay 5M operates at this time indicating that relay 359 functionedproperly, ground from the upper winding of relay 509 is not removed,thereby preventing the operation of this relay and the connection ofground to conductor 6l2 so that the relays of Fig. 5 can start testingthe trunk group. A similar result is obtained if relay 651 fails tooperate and relay 6B5 operates, or if both relays 6G5 and 691 fail tooperate. If the trunk groups are arranged on a split horizontal basis,relays 555 and 608 function in the same manner as relays 555 and 601,removing ground from the upper winding of relay 609 only if both relaysoperate. If the marker is now operating on a first trial, relay 609 willbe normal, and due to the non-operation of relay 659 the call will beblocked. After an interval the timing mechanism 440, which begins tocount time when the marker is taken in use, causes a release signal tobe sent over conductor 4 to the sender M18. The sender then releasesitself from the marker, and the marker restores to normal. This isdescribed in detail in the Carpenter patent and in the Carpenterapplication aforesaid.

The sender will now select another marker for a second trial, and thiswill cause slow releasing relay 602 in the second marker to operate byreason of a signal received from the sender I08. Relay 652 in operatingcloses a circuit from ground through its upper make contacts and themultipled windings of relays EDI and 600 to battery. These relays nowoperate and lock to ground 6H5. Assume now, as a basis of description,that the trunk group is arranged on a nonsplit basis and that relay 60'!operates due to the grounding of conductor 3H which is extended to theodd frame, but that relay 605 associated with the even frame due to sometrouble condition fails to operate. A circuit is then closed to operaterelay 694, which circuit extends from battery through the winding ofrelay 604, upper break contacts of relay 655, upper inner operatedcontacts of relay 68! to ground BIB on the operated lower inner contactsof relay 530. The operation of relay 6M opens the operating circuit ofrelay 832, which starts to release. This relay is arranged to releaseslowly so that on normal sec- 0nd and third trials of the marker it willnot have time to release if there is the usual difference in timebetween the operation of relays 6B5 andfiifl, which would be the resultof a difference in operating time of relays SIS and SIS. On second andthird trial calls, relay 604 may be expected to operate momentarily, butit will release before relay 5U2'has had time to release and with itslower break contacts close a locking circuit for relay 604, whichlocking circuit will be hereinafter described. Assuming now relay 604oper ated, as before stated, due to a trouble condition on the evenframe, it then looks through its up per inner make contacts, lower breakcontacts of relay 602 and lower inner make contacts of relay 600 toground 6|6.- Ground on the operated contacts of relay 60! will beextended through the upper break contacts of relay 602, lower makecontacts of relay 604, over conductor 528 and through the winding ofrelay 5|! to battery. Relay 5|l now operates and connects ground throughits right contacts to the windings of relays 50| and 509, and of otherrelays, not shown, corresponding to trunks on the even frame, which byassumption was in trouble. This causes all trunks on the even frame toappear busy to the trunk testing circuit. If now relay 60'! fails tooperate and relay 605 operates indicating that trouble exists on the oddnumbered frame, then relay 603 operates in a circuit from batterythrough its winding, upper break contacts of relay 60'!, upper makecontacts of relay 605, lower inner'make contacts of relay 600 to ground6| 6. Relay 603 looks through its upper make contacts to ground 5|6through the lower break contacts of relay 602 and the lower inner makecontacts of relay 600. Relay 603 closes a circuit for operating relay5") which circuit extends from battery through the winding of relay 5|6,over conductor 529, through lower make contacts of relay 603, upperbreak contacts of relay 602 to ground on the make contacts of relay 60LRelay 5|6 connects ground through its right make contacts to thewindings of relays 505 and 5|3, and of other similar relays, not shown,of the odd frame. Consequently, the trunk testing circuit functions nowas if all trunks on the odd numbered frame were busy. Since relays 603and 604 cannot oper-' ate simultaneously as their respective operatingcircuits are both open when relays 60! and 605 are both operated, itfollows that relays 5|6 and 5|! cannot both begoperated at the sametime. When relay 5| 6 operated indicating trouble on the odd numberedframe, the left inner contacts of this relay connected togetherconductors 533 and 534 which connect respectively with conductors 3!!and 309, extending to the windings of relays 60! and 605 of the even andodd frames respectively. Since the trouble is on the odd frame, relay60! did not operate, but now the Winding of relay 60'! is joined overconductors 533 and 534 with the grounded winding of relay 005. Relay 60!now operates and ground is accordingly removed from the upper winding ofrelay 609 as hereinbefore described. The operation of relay 60'! opensthe operating circuit of relay 603, but this relay now holds on itslooking circuit. Relay 609 operates and connects ground to conductor 6|2through the upper contacts of relay 6|0, which is operated through theseries chain connection of the upper normally closed contacts of relays50L 505,509, and 5|3. A trunk on the even frame is now selected asbefore described. If the trouble is on the even numbered frame thenrelay 5!! in operating also connects together with its inner leftcontacts conductors 533 and 534. In this case relay 605 not beingoperated from the connecting relay 3|8, is operated now by the ground onthe winding of relay 60'!. Relay 609 operates as before and a trunk onthe odd numbered frame is selected.

When the trunk group is arranged on a split Relays 605 and 60'! are usedfor the non-' split, and relays 606 and 608 for the split horizontalarrangements of the office frame. If now one of the relays of the splitarrangement should be operated at the same time as one of the relays ofthe non-split arrangement, then the marker will time out due to thenon-removal of ground from the upper winding of relay 609, whichconsequently does not operate to start the trunk selection. This isbecause each of the heretoforementioned relays is provided with lowerinner make contacts so connected that when any two dissimilar relays areoperated, the upper winding of relay 609 is connected to ground inseries with the two aforesaid operated make contacts. To illustrate,assume that the pair of relays V605 and 60! is properly operated, butthat relay 606 is at the same time improperly operated. The upperwinding of relay 609 now remains connected to ground 6M through lowerinner make contacts of relays 005 and 606 and relay 609 fails tooperate. lays 60! and 608 only are operated. The upper winding of relay609 is now connected to ground 6|3 through lower inner make contacts ofrelays 60'! and 608. Similar circuits may be traced for othercombinations of operated dissimilar relays.

What is claimed is:

1. In a telephone system,'a group of trunks, a marker arranged to make aplurality of trials to extend a call over said group of trunks, a seriesof test relays in said marker for testing the respective trunks of saidgroup, and a circuit arrangement associated with said series of testrelays for selecting the idle trunk nearest one end of the group on afirst trial by the marker and for selecting the idle trunk nearest theother end of the group on a subsequent trial by the marker.

2. In a telephone system, a group of trunks, a marker arranged to make aplurality of trials to extend a call over said group of trunks, aplurality of test relays in said marker for making a simultaneous testof all the trunks in said group, a selecting circuit cooperating withsaid test relays to examine the tested trunks in a definite order if themarker is engaged in a first trial and to examine said trunks in adifferent order if the marker is engaged in a subsequent trial, andmeans controlled by said selecting circuit to select for use the firstidle trunk encountered.

3. In a telephone system, a group of trunks, a marker arranged to make aplurality of trials to extend a call over said group of trunks, aplurality of test relays in said marker, means for connecting said testrelays respectively to said trunks to make a simultaneous test thereof,all relays corresponding to busy trunks operating and thosecorresponding to idle trunks remaining deenergized, a selecting circuitcooperating With said test relays for selecting an idle one of saidtrunks, means for extending said selecting circuit to the contacts ofsuccessive test relays in a given order to select the first idle trunknearest one end of said group on a particular trial by said marker, andmeans for extending said selecting circuit to the contacts of successivetest relays in the reverse order to select the first idle trunk nearestthe opposite end of said group on a different trial by said marker.

4. In a telephone system, two selector switches, a group of trunksdivided into two subgroups, the first of which appears in the first ofsaid switches and the second of which appears in the second switch, aset of links leading to said first switch and a second set of linksleading to the second switch, means for testing all of said trunks andfor selecting one in either subgroup, means for testing the linksreaching the corresponding switch, means efiective if all of the testedlinks are busy for repeating the test of said trunks and for preventingthe selection of a trunk in the subgroup containing the first selectedtrunk, and means effective if an idle trunk is found in the othersubgroup on said second test for testing the links of the set reachingthe switch corresponding to said other subgroup.

5. In a telephone system, a pair of selector switches, a group of trunksdivided into two subgroups, one of which appears in the first switch andthe other in the second switch, a plurality of link paths extending tosaid first switch, a second plurality of link paths extending to thesecond switch, means for testing all of said trunks and for selecting anidle one in either the first or the second subgroup, means for testingthe link paths extending to the corresponding switch, means effective ifall of the tested link paths are busy for repeating the test of all ofthe trunks in said trunk group, means for rendering artificially busyall trunks in the subgroup containing the first selected trunk to causethe selection of an idle trunk in the other subgroup on the retest, andmeans effective if an idle trunk is found on retest in said othersubgroup for testing the link paths extendingtothe corresponding switch.

6. In a telephone system, a pair of automatic switches, a group oftrunks divided into subgroups, said subgroups appearing respectively insaid automatic switches, a marker arranged to make repeated trials toestablish a connection over said trunk group, means for establishing aconnection between the marker and both of said switches, means in themarker for testing simultaneously all of the trunks in said group, meansfor testing the condition of the connections established between themarker and said switches, means effective if the connection between themarker and either of said switches is unsatisfactory on a first trial bythe marker for causing the marker tobring about a second trial, andmeans effective if on a subsequent trial by the marker the test of theconnection to either of said switches is unsatisfactory for causing alltrunks on such switch to appear busy to the marker and for causing themarker to proceed with the selection of an idle trunk in the subgroupappearing in the other of said switches.

'7. In a telephone system, a pair of automatic switches, a group oftrunks divided into two subgroups, one of which appears in the firstswitch and the other in the second switch, a common marker arranged tomake repeated trials to establish a connection over said trunk group,means efiective when the marker is seized for establishing a connectionbetween the marker and both of said switches, testing means in themarker for making a simultaneous test of the trunks in both subgroups,means in the marker for making separate tests of the condition of theconnections established between it and said switches, means effective ifeither connection between the marker and one of said switches testsunsatisfactory or if both connections are unsatisfactory on a firsttrial of the marker for causing the marker to release and bring about asecond trial, and means effective if on a subsequent trial by the markerthe test of the connection to either one of said switches isunsatisfactory for causing all trunks in the subgroup appearing on saidswitch to test artificially busy to the marker and for causing themarker to proceed with the test of the subgroup of trunks appearing inthe other of said switches.

RALPH E. HERSEY.

